Predict the output · TypeScript

Numeric Enums at Runtime

Medium Predict the output Seen at Microsoft, Shopify

What does this print?

enum Color {
  Red,
  Green,
  Blue = 10,
  Purple,
}
console.log(Color.Green, Color.Purple, Color[10]);

```
1 11 Blue
```
```
Green Purple 10
```
```
1 4 Blue
```
```
1 11 undefined
```

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Solution

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The output is:

1 11 Blue

Numeric enum members auto-increment from the previous value: Red = 0, Green = 1, Blue = 10, Purple = 11. Numeric enums also get a reverse mapping, so Color[10] is "Blue".

Enums are one of the few TypeScript features that emit runtime code. Many teams prefer union types ("red" | "green") or as const objects for that reason.

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